I had recently downloaded the installer which was version 1.5.1 afew days ago. I just earlier downloaded the previous version 1.4.1 and it seems to be working okay now. No cpu spikes and the on/off button works.

I uninstalled my exisitng version first and then installed the 1.4.1 version, it differs in that it suggest to put the VST and shortcuts (Windows 7 user here) into the foler "SPL" and not "Plugin Alliance"...think this was an update to all there plugins recenlty. I changed the defaults to put it to the Plugin Alliance folder as before.

I've closed my Ableton down and re-opened it and it still seems to function well.

Just installed version 1.4.1 of Twin Tube and man.. it works and it's CPU usage is MUCH lower than 1.5.1. This old version uses only about 3% CPU on my laptop whereas the new version uses over 10%. That's a whopping 3 times more CPU.

Not sure about the sound yet.. might be placebo. I'll do some renders and invert phase to check sound.

I tried installing Presonus Studio One Demo, got the same problem with TwinTube 1.5.1 - about 25% cpu per instance till the 4th one went over 100% in the Studio One Perf monitor and got a gawd-awful ugly sound. It also installed VST3 and VST 2.4 versions of TwinTube , I think I was using VST3 of TwinTube. Not sure which I was using in Reaper.

Anyway - gotta get some dog-food, will try 1.4.1 later - sounds like an interesting development!

1.5.1 sounds quite a bit better. My guess is that it's 4x oversampled or something compared to 1.4.1. I've phase cancelled them and at various identical settings (you can install both plugins side by side, just make sure you rename the .dll file of one of them before installing the other). The difference seems to be program dependent (meaning they probably tweaked the algorithm or something) and ranges around -40dBFS to -60dBFS. This is a significant difference and you can clearly hear how transients are treated differently from one another (by listening to the residue of the phase cancellation.. aka the difference).

Interesting things.. unfortunately this means going back to 1.4.1 isn't really an option, unless you happen to like the sound of that one more (I don't).

Well, I just installed the 1.4.1, and it does work, lower CPU use and no spikes. But even a cursory listen reveals that the newer version is superior - sonically speaking. Whether this is due to oversampling, I can't say, but the distortion is a good deal harsher and fuzzier on the old one.